Supergirl opened to just $18 million on Friday — landing in second place behind Disney and Pixar's Toy Story 5, which pulled in $21 million from 4,425 screens — and is tracking toward a $40-50 million weekend. That's a steep comedown from last summer, when James Gunn's Superman debuted to $125 million on its way to $618 million worldwide. The $170 million DC gambit arrives saddled with a 57% Rotten Tomatoes critics score. Audiences have...